The present invention relates to a laser imaging device which deflects a plurality of laser beams having different wavelengths to scan on an objective surface to form an image thereon.
Conventionally, a laser imaging device such as a direct imager, a laser photo plotter or the like has been used for forming a circuit pattern on a base plate for manufacturing a printed circuit board, a semiconductor device or the like. Such an imaging device is constructed such that a laser beam emitted by a light source is modulated, and then deflected using a polygonal mirror. The deflected beam scans on an objective surface (i.e., the surface of a base plate), on which photosensitive material is applied, to form a circuit pattern thereon. Since the laser beam impinges on the objective surface directly, a gas laser (e.g., Argon laser), which oscillates continuously at high power is used as the light source.
Further, conventionally, in order to obtain a relatively high exposure amount, a laser source, which emits a laser beam having a plurality of wavelength components, has been employed. When such a beam is used, however, if a scanning optical system of the laser imaging device has chromatic aberration, beam spots to be formed on the objective surface are formed at different positions depending on the wavelengths. Therefore, in the scanning optical system of the laser imaging device employing such a light source, the optical systems thereof is constructed such that the chromatic aberration is compensated.
Recently, there is a requirement that a relatively wide area is scanned at a high speed. For example, Japanese patent provisional publication HEI 10-142538, entitled as xe2x80x9ca laser imaging device having a multi-head scanning optical systemxe2x80x9d discloses a laser imaging device of such a type. In the laser imaging device described in the publication, two scanning optical systems, which are arranged in the main scanning direction, are provided. The laser beam having a single wavelength this modulated by a modulator, and the modulated beam is alternately directed to impinges on two scanning optical systems, which are arranged in the main scanning direction, so that a relatively wide area is exposed to light.
In the laser imaging device provided with two scanning optical systems as described above, if a light source, which emits a laser beam including a plurality of components having different wavelengths, is employed, it becomes necessary that the chromatic aberration of each scanning optical system is compensated, which complicates the structure of the scanning optical system as a whole, and increases the manufacturing cost.
It is therefore an object of the present invention to provide an improved laser imaging device provided with a laser source that emits a laser beam including a plurality of wavelength components, and a plurality of scanning optical systems arranged in the main scanning direction, and the structure of the optical systems will not be complicated.
For the above object, according to the invention, there is provided a laser imaging device, which is provided with at least one laser source that emits a laser beam including a plurality of wavelength components, at least one dividing optical system that spatially divides the laser beam into the plurality of wavelength components, at least two modulating optical systems, at least two of the plurality of wavelength components divided by the dividing optical system being modulated by at least two modulating optical systems, respectively, and at least two scanning optical systems. At least two of the plurality of wavelength components respectively modulated by the at least two modulating optical systems are caused to scan on at least two different areas of an objective surface by the at least two scanning optical systems.
With the above configuration, since the beams having different wavelengths are incident on different scanning optical systems, it is not necessary to compensate for the chromatic aberration.
Optionally, the at least one laser source includes a plurality of laser sources, and the at least one dividing optical system includes a plurality of dividing optical elements corresponding to the plurality of laser sources, respectively.
The laser imaging device is further provided with a beam combining system that combines beams having the same wavelength.
Further optionally, each of the at least two modulating optical systems includes an acousto-optical-modulator.
Still optionally, each of the at least two modulating optical system includes a beam dividing element that divides an incident beam into a plurality of divided beams.
In this case, each of the at least two modulating optical systems includes a multi-channel acousto-optical-modulator that modulates the plurality of divided beams independently from each other.
Still optionally, each of the at least two modulating optical systems is provided with a relay lens that adjusts a diameter of each of the wavelength components divided by the at least one dividing optical system, a collective lens that converges each of the plurality of divided beams divided by the beam dividing element on positions in the vicinity of the multi-channel acousto-optical-modulator, and a collimating lens that collimates the beams modulated by the multi-channel acousto-optical-modulator.
In particular case, each of the at least two scanning optical system may include a polygonal mirror that deflects the modulated beams to scan. In this case, each modulating optical system may include a piezo mirror, inclination of which is controlled to compensates for facet error of the polygonal mirror.
Further optionally, the at least one light source includes an Argon laser source that emits a laser beam including at least two components whose wavelengths are close, output power of the at least two components being substantially the same.
In the laser imaging device described above, the wavelengths of at least two components are approximately 351.1 nm and approximately 363.8 nm, so the wavelength-difference is small. Alternatively, at least two components may include a component whose wavelength range includes approximately 351.1 nm and approximately 351.3 nm, and another component whose wavelength is approximately 363.8 nm.